Sonar transducer

ABSTRACT

A sonar transducer mounted on a probe inserted in a vessel or container emits a sonar wave for measuring the level of fluid interfaces within the vessel or container. The sonar transducer includes a housing closed by a diaphragm at one end. A piezoelectric crystal located within the housing is biased against the diaphragm and is electrically connected to an energizing source. The travel time of the sonar wave emitted by the piezoelectric crystal and reflected by the fluid interfaces is measured. The sonic wave measurements are communicated to a microprocessor and the levels of the liquid interfaces within the vessel or container are calculated.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of prior application Ser. No.10/641,874, filed Aug. 15, 2003, now U.S. Pat. No. 6,990,046, and claimsthe benefit of U.S. Provisional Application Ser. No. 60/403,628, filedAug. 15, 2002, which application is incorporated herein by reference.

BACKGROUND OF THE DISCLOSURE

The present invention relates to generally to industrial interfacemeasurement devices, and more particularly to a measurement device usinga sonar transducer to measure fluid to fluid, fluid to solid and fluidto gas interfaces in various industrial applications.

It is commonly known in the art that a piezoelectric crystal can be usedas a transducer to emit a sonic or ultrasonic acoustic wave when excitedby an AC voltage. Such a device may be used for determination of thedistance of an object through the placement of a detector which senseswhen the emitted acoustic wave has reached the detector. Based on thetime it takes the acoustic wave to reach the detector as well as thespeed of the acoustic wave within the transmission medium, the distancefrom the source of the wave to the detector may be calculated. It isalso known that the level of a liquid within a storage container may bedetermined through the use of a similar device and the concept of echoranging. For example, U.S. Pat. No. 3,834,233 to Willis et al. disclosessuch a system. The system includes an ultrasonic transducer mounted atthe top of a storage tank which directs an acoustic wave through the airdown into a storage tank toward the surface of the liquid to bemeasured. Once the acoustic wave reaches the surface of the liquid, thewave's frequency is such that it will be reflected back toward thedevice which is equipped with a receiver to detect the reflected wave.The receiver thus detects the echo from the surface of the liquid and,based on the time for the signal to reach the surface of the liquid andreturn, calculates the distance from the ultrasonic transducer to thesurface of the liquid.

However, such systems are not without their problems. Because suchsystems typically transmit the acoustic wave through a gaseous mediumabove the surface of the liquid to be measured, lower operatingfrequencies are required in order that the transmitted wave will bereflected at the liquid surface. These lower operating frequencies areless accurate in making distance measurements than higher frequencies.Such prior art systems have also been plagued by false signals receivedat the detector which did not originate from the device (such as outsidenoise) or which were not reflected from the material surface (i.e.,reflected from the sides of the storage container). Prior art systemshave also been plagued by the harsh conditions typically found withinmany industrial storage containers, particularly those storing corrosivesubstances. The quality of the device operation and the length of timethese prior art detectors are able to maintain operation in such harshenvironments result in their frequent malfunction and necessaryreplacement. Corrosive environments are especially hard on devicesemploying welded joints, epoxies or adhesives in their structures sinceit is at these points that corrosive effects are first manifested. Notonly does the corrosive material itself decrease the operating life ofsuch devices, but also changes in the operating environment of thedevice, including temperature and pressure changes, adversely affectsuch devices.

Finally, such prior art systems have been adversely affected byexcessive dispersion of the emitted ultrasonic measurement beam suchthat the emitted signal is not strong enough to be reflected back to thedevice from a great distance (i.e. when the material in the storagecontainer is at a low level). A weak emitted signal may also be causedby poor signal transfer within the device from the crystal to theemitting diaphragm. Another cause of poor device performance occurs whenthe detector radiates the transmitted signal in a number of directions,rather than in a narrow, focused beam, thereby increasing thepossibility of falsely detecting reflected waves (e.g. from the storagecontainer walls). The prior art has employed a variety of dampingmaterials in various configurations to try and alleviate some of theseproblems. For example, U.S. Pat. No. 5,121,628, issued to Merkl et al.employs one such damping approach using lead pellets. For better signaltransfer, the prior art has used bonding agents such as epoxies orsolder, as disclosed in U.S. Pat. No. 4,000,650, issued to Snyder

It is, therefore, an object of this invention to provide a sonartransducer which detects the presence of an object or material and isresistant to malfunction or deterioration caused by changingtemperature, changing pressure, corrosive environments, or a combinationof these conditions.

It is another object of the present invention to provide a sonartransducer which is installed within the fluid it is designed tomeasure.

It is still another object of the present invention to provide a sonartransducer which has greater accuracy than that provided by existingdevices.

It is yet another object of the present invention to provide a sonartransducer with improved signal transfer, focus and strength resultingin a larger measurement range.

It is still another object of the present invention to provide a sonartransducer having an improved, smaller size.

It is yet another object of the present invention to provide a sonartransducer which can measure the material level of the contents within astorage container.

It is another object of the present invention to provide a sonarfluid-level detector which may be installed from the top, bottom, orside of a storage container.

SUMMARY OF THE INVENTION

In accordance with the present invention a sonar transducer mounted on aprobe inserted in a vessel or container emits a sonar wave for measuringthe level of fluid interfaces within the vessel or container. The sonartransducer includes a housing closed by a diaphragm at one end. Apiezoelectric crystal located within the housing is biased against thediaphragm and is electrically connected to an energizing source. Thetravel time of the sonar wave emitted by the piezoelectric crystal andreflected by the fluid interfaces is measured. The sonic wavemeasurements are communicated to a microprocessor and the levels of theliquid interfaces within the vessel or container are calculated.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features, advantages andobjects of the present invention are attained can be understood indetail, a more particular description of the invention brieflysummarized above, may be had by reference to the embodiments thereofwhich are illustrated in the appended drawings.

It is noted, however, that the appended drawings illustrate only typicalembodiments of this invention and are therefore not to be consideredlimiting of its scope, for the invention may admit to other equallyeffective embodiments.

FIG. 1 is a side view of the device of the present invention;

FIG. 2 is a section view of a preferred embodiment of the ultrasonictransducer of the present invention;

FIG. 3 is a section view illustrating the installation of the device ofthe present invention within a storage container; and

FIG. 4 is a section view of an alternate embodiment of the ultrasonictransducer of the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Referring first to FIG. 1, the interface measurement apparatus of theinvention is generally identified by the reference numeral 10. Theapparatus 10 includes an electronics housing 12, a tank connector 14, ashaft 16 and a transducer 18 mounted on the distal end of the shaft 16.The transducer 18 is electrically connected to the electronics housing12 by a wire extending through the shaft 16.

Referring now to FIG. 2, the transducer 18 is shown in greater detail.The transducer 18 includes a housing 20 having a generally cylindricalconfiguration open at a forward end thereof. The transducer 18 ismanufactured of materials suitable to withstand harsh industrial demandsand comply with regulatory requirements. Components may be selected ofmaterials for specific application requirements and needs, such as food,corrosion, contamination, etc. In the preferred embodiment, the housing20 material is SS316. Other suitable metals may also be used.

A diaphragm 22 is mounted to the forward end of the housing 20. Thediaphragm 22 is fabricated from rolled metal sheet. However, thematerial choice for the diaphragm 22 depends on application requirementsand environmental factors. The diaphragm 22 has a generally circularconfiguration cut out of the rolled metal sheet and stamped to include acircumferential flange 24 and a central disk portion 26. An inclinedcircumferential wall portion 28 joins the disk portion 26 to the flange24. The diaphragm 22 is welded to the housing 20 at welding joint 30. Asafety ring 32 is welded on top of the peripheral edge of the flange 24to control heat related stress and deformation of the diaphragm 22.

Referring still to FIG. 2, a piezoelectric crystal disk 34 is locatedinside the housing 20 adjacent to the diaphragm 22. The crystal 34 is agenerally solid cylindrical disk having flat opposed surfaces generallycircular in cross-section. The crystal 34 is in facing contact with theinside surface of the diaphragm 22 at one end and in facing contact withan isolation washer 36 at the opposite end thereof. A retaining washer38 is biased against the isolation washer 36 by a spring 40 locatedbetween the retaining washer 38 and an internal circumferential shoulder44 formed in the lower end of the transducer housing 20. An O-ring 41 isreceived in a circumferential internal groove 43 formed in the housing20 near the forward end thereof. The O-ring 41 aids in centering thecrystal 34 and forms a seal therewith to prevent fluid, such as oil, inthe lower portion of the housing 20 from entering the upper portion ofthe housing 20 and coming into contact with the diaphragm 22.

A connector plug 42 depends downwardly from the lower end of the housing20 and is integrally formed with the housing 20. The connector plug 42is externally threaded for connection to the shaft 16. The connectorplug 42 includes an axial passage 48 which terminates at the shoulder 44of the housing 20 at the upper end thereof and the lower end of thepassage 48 opens into an enlarged bore 45 formed in the connector plug42.

The isolation washer 36 and retaining washer 38 include centrallylocated holes 56 and 57, respectively. The holes 56 and 57 providesaccess for electrically connecting the crystal 34 to a power source toproduce a sonic wave. The crystal 34 is electrically connected to an ACvoltage source by a wire 66 extending through the tube 58 and solderedto the crystal 34 at 67. The wire 66 is also soldered to the lower endof the tube 58. The tube 58 is inserted into the passage 48 and sealedtherein by a glass bushing 64 which is located about the tube 58 in theaxial passage 48 extending through the connector plug 42. The bore 43 ofthe connector plug 42 is filled with epoxy 45, which epoxy 47 completelyencapsulates the lower end of the tube 58 and a portion of the wire 66.The epoxy 47 provides some flexibility about the wire 66 so that it maymove slightly without breaking.

The internal cavities of the transducer housing 20 are filled with asmall amount of non-conductive and non-corrosive fluid through the tube58 prior to welding the wire 66 to the lower end of the tube 58. Thewire 66 functions as the positive lead for energizing the crystal 34.The housing 20 functions as the negative lead to complete the ACcircuit. The crystal 34 may be biased with AC voltage at a highfrequency so that it is energized and begins to vibrate. Vibration ofthe crystal 34 against the diaphragm 22 produces a sonic wave as isknown in the art.

Referring now to FIG. 4, an alternate embodiment of the invention isshown. The transducer 80 of FIG. 4 is substantially the same as thetransducer 18 described above, so the same reference numerals areutilized to identify like components. In the embodiment of FIG. 4, thewire 66 is soldered at the lower end of the tube 58. The tube 58 extendsto the crystal 34 and is provided with a secondary spring spacer 60mounted on the distal end thereof. The secondary spring spacer 60 isforced against the crystal 34 by a secondary spring 62 journaled aboutthe tube 58 and compressed between the spring spacer 60 and the shoulder44 of the housing 20. In the embodiment of FIG. 4, the tube 58 functionsas the positive lead for energizing the crystal 34. The housing 18functions as the negative lead to complete the AC circuit.

Referring now to FIG. 3, use of the interface measurement apparatus 10of the invention is illustrated. The transducer 18 and shaft 16 of theapparatus 10 are inserted through an opening in a storage tank 70. Thetank connector 14 is threaded in the opening for securing the apparatus10 to the storage tank 70. The electronic housing 12 remains on theoutside of the storage tank 70 and is connected to a microprocessor anddisplay. Upon set up and calibration of the apparatus 10, the crystal 34is energized and emits it sonar wave toward the surface of the liquid tobe measured. The signal emitted by the transducer crystal 34 travelsthrough the liquid and is reflected from the fluid interface(s), solidsin the fluid or the inner surface of the storage tank 70. The traveltime of the sonar wave is measured and the level of the liquidinterface(s) is calculated in a known manner. Multiple interfaces may bedetected and measured, and the apparatus 10 of the invention may bemounted at various locations about the storage tank 70.

While a preferred embodiment of the invention has been shown anddescribed, other and further embodiments of the invention may be devisedwithout departing from the basic scope thereof, and the scope thereof isdetermined by the claims which follow.

1. A sonar transducer for detecting the level of liquid to liquid andliquid to solid interfaces in a container, comprising: a) a housing; b)a diaphragm for emitting a sonar wave through a fluid, said diaphragmbeing welded across an end of said housing; c) an annular ringsurrounding said diaphragm; d) a piezoelectric crystal located withinsaid housing adjacent to said diaphragm; e) means for biasing saidpiezoelectric crystal against said diaphragm; and f) means forelectrically connecting said piezoelectric crystal to an energizingsource.
 2. The sonar transducer of claim 1 wherein said biasing meanscomprises a spring mounted within said housing.
 3. The sonar transducerof claim 2 including an isolation disk located adjacent saidpiezoelectric crystal.
 4. The sonar transducer of claim 1 including asingle electrical connector connecting said piezoelectric crystal tosaid energizing source.
 5. The sonar transducer of claim 3 including aretaining washer located adjacent said isolation disk.
 6. The sonartransducer of claim 1 wherein said biasing means comprises primary andsecondary springs mounted within said housing.